Presumably this has the same problems of parser interaction as r49399, for example, in a site notice disabling all content conversion on the wiki. Or maybe it's the other way around, in an article disabling conversion of the site notice. And the use of $wgParser->UniqPrefix() could have some interesting consequences if the site notice is generated before the parser is initialised, such as suppressing conversion of all text matching /[\-a-zA-Z0-9]+/.
Also the convert() call should have been inside the profiling section.